Code multiplexing transmitting apparatus

ABSTRACT

A code multiplexing transmitting apparatus spread-spectrum modulates transmission data of a plurality of channels by spreading codes that differ from one another, combines the spread-spectrum signals of each of the channels and transmits the resultant spread-spectrum modulated signal. A spread-spectrum modulating unit for each channel includes a phase shifter for shifting, by a predetermined angle channel by channel, the phase of a position vector of the spread-spectrum modulated signal of each channel. As the result of such phase control, the phases of pilot signal portions of the spread-spectrum modulated signals of the respective channels are shifted relative to one another so that the peak values of the code-multiplexed signal can be suppressed.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a code multiplexing transmittingapparatus and, more particularly, to a code multiplexing transmittingapparatus for spread-spectrum modulating signals of a plurality ofchannels by respective ones of codes that differ from one another,combining the spread-spectrum modulated signals of each of the channelsand transmitting the resultant spread-spectrum modulated signal.

[0002] Wireless access using CDMA (Code Division Multiple Access) hasbeen studied and is being put to use as the next generation of digitalmobile communication. CDMA is a method of multiple access usingspread-spectrum communication. Specifically, transmission information ofa plurality of channels or users is multiplexed by coding andtransmitted over a transmission path such as a radio link.

[0003] Spread-spectrum communication is a method of modulation that isdifferent from ordinary narrow-band modulation. In spread-spectrumcommunication, the bandwidth of a signal after modulation is made verylarge in comparison with that of the narrow band in narrow-bandmodulation. With spread-spectrum communication, two-stagemodulation/demodulation is performed in the transceiver.

[0004]FIG. 16 is a structural view illustrating the operating principleof a transmitter in spread-spectrum communication. Shown in FIG. 16 area modulator 1 such as a (phase-shift keying) PSK modulator, a spreadingcircuit 2, a power amplifier 3 and an antenna 4. The positions of themodulator 1 and spreading circuit 2 may be interchanged. The spreadingcircuit 2 includes a spreading code generator 2 a for outputting arectangular spreading code sequence (see FIG. 17) that randomly takes onlevels of ±1 referred to as a pseudorandom noise (PN) sequence, and amultiplier 2 b for multiplying digital transmission data, which has beenmodulated by the modulator 1, by the spreading code.

[0005] As shown in FIG. 17, the speed at which the spreading codechanges (namely duration Tc of the rectangular wave) is set so as tochange over at a very high rate in comparison with symbol changeoverspeed, (one bit interval T of the PSK-modulated signal) of thenarrow-band modulated signal that is modulated by the spreading code.That is, T>>Tc holds. The duration of T is referred to as the “bitduration”, the duration of Tc is referred to as the “chip duration”, andthe reciprocals of these are referred to as the “bit rate” and “chiprate”, respectively. The ratio of T to Tc (i.e. T/Tc) is referred to asthe “spreading ratio”.

[0006] The spectrum distribution of a spread-spectrum modulated signalexhibits the shape of a sinc function, as shown in FIG. 18. Thebandwidth of a main lobe ML is equal to twice the chip rate (i.e.ML=2/Tc), and the bandwidth of a side lobe SL is 1/Tc. Since the PSKsignal prior to spread-spectrum modulation is an ordinary PSK signalmodulated at the bit rate 1/T, the occupied bandwidth is 2/T.Accordingly, if the occupied bandwidth of the spread-spectrum modulatedsignal is made the bandwidth (=2/Tc) of the main lobe, the bandwidth ofthe original PSK-modulated signal will be broadened T/Tc times byapplying spread-spectrum modulation. The energy is diffused as a result.FIG. 19 is an explanatory view illustrating the manner in whichbandwidth is enlarged by spread-spectrum modulation. Shown in FIG. 19are a narrow bandwidth-modulated signal NM and a spread-spectrummodulated signal SM.

[0007]FIG. 20 is a structural view illustrating the operating principleof a receiver in spread-spectrum communication. Shown in FIG. 20 are anantenna 5, a wide-band bandpass filter 6 for passing only signals ofnecessary frequency bands, a de-spreading circuit 7, a bandpass filter 8and a detector circuit 9 such as a PSK demodulator. The de-spreadingcircuit 7 has a construction identical with that of the spreadingcircuit 2 on the transmitting side and includes a spreading codegenerator 7 a for outputting a rectangular spreading code sequence thesame as that on the transmitting side, and a multiplier 7 b formultiplying the output signal of the bandpass filter 6 by the spreadingcode.

[0008] The wide-band reception signal sent to the receiver is restoredto the original narrow-band modulated signal via the de-spreadingcircuit 7 similar to the spreading circuit on the transmitting side.This is followed by the generation of a baseband waveform via thedetector circuit 9, which is of the ordinary type. The reason why thenarrow-band modulated signal is obtained by the de-spreading circuit 7is as set forth below.

[0009] As shown in FIG. 21, let a(t) represent the modulated wave on thetransmitting side, c(t) the spreading code sequence (spreading code) andx(t) the transmitted waveform. These are related as follows:

x(t)=a(t)·c(t)

[0010] If attenuation and the effects of noise during transmission areneglected, the transmitted waveform x(t) arrives on the receiving sideintact. The spreading code sequence used by the de-spreading circuit 7has a waveform exactly the same as that -of the spreading code used inspread-spectrum modulation on the transmitting side, as mentioned above.Accordingly, the output y(t) of the de-spreading circuit 7 is given bythe following equation:

y(t)=x(t)·c(t)=a(t)·c ²(t)

[0011] The output signal y(t) enters the bandpass filter 8. Passing thissignal through the bandpass filter is the same as integrating thesignal. Thus the output of the bandpass filter is given by the followingequation:

∫y(t)dt=a(t)·∫c ²(t)dt

[0012] The integral on the right side of this equation is anautocorrelation value obtained when the shift in time is made zero. Theautocorrelation value is unity. Accordingly, the output of the bandpassfilter is a(t) and the modulating information signal is obtained.

[0013] Code division multiple access (CDMA) is a method of communicationusing a different spreading code for each channel or user, whereby theinformation transmitted on the respective channels is multiplexed by thecodes. FIG. 22 is a diagram for describing the principle of CDMA on twochannels. Shown in FIG. 22 are a transmitter TR in, which CH1 is a firstchannel, CH2 a second channel and CMP a combining unit, and first andsecond receivers RV1, RV2, respectively.

[0014] An important point in CDMA is the “similarity” of the spreadingcodes used by each of the channels. When almost identical spreadingcodes are used by each of the channels, the channels interfere with eachother severely. A so-called “correlation value” is a measure of thedegree to which interference between channels occurs. The correlationvalue is defined by the following equation with respect to two waveformsa(t) and b(t):

R=∫a(t)·b(t)dt T: period

[0015] The integration is carried out over one period T of a(t), b(t).We have R=1 when a(t) and b(t) are exactly identical waveforms and R=−1when the waveforms are of opposite signs. On the average, looking at oneperiod, the value of R obtained is zero when there is no relationshipbetween the value of a(t) at a certain time and the value of b(t) at thesame time.

[0016] Consider the first receiver RV1 in a situation where CDMA isperformed using, as the spreading code, two waveforms c₁(t) and c₂(t) ofsuch a combination that the correlation value R is zero. The signalsfrom the first and second channels CH1 and CH2 arrive at the firstreceiver RV1. When the first receiver RV1 de-spreads the receivedsignals using the code c1 (t), a bandpass filter 8 ₁ outputs a signalrepresented by the following equation:

∫{a ₁(t)c ₁(t)c ₁(t)+a ₂(t)c ₂(t)c ₁(t)}dt

[0017] The ∫{a₂(t)c₂(t)c₁(t)}dt part of this is zero because thecorrelation value between c₂(t) and c₁(t) is zero. Further, ∫c_(1 (t)c)₁(t)dt is unity since this is an autocorrelation value in which thedisplacement in time is zero. Accordingly, the output of the bandpassfilter 8 ₁ of the first receiver RV1 is a₁(t) and the influence of thesignal making use of c₂(t) as the spreading code is entirely absent. Thesame is true for the second receiver RV2. This will hold even if thenumber of simultaneously connected communication channels is increased.However, it is required that the correlation value be zero for thespreading codes of all combinations.

[0018] In mobile wireless communication, wireless base stations emitradio waves (generate spreading code sequences) at the same timing (i.e.synchronously). It will suffice, therefore, to select spreading codesequences in such a manner that the correlation value will be zerobetween the spreading code sequences. It should be noted that since onewireless mobile station will not emit radio waves at the same timing asother wireless mobile stations, mutual influence cannot be measuredmerely by the correlation value. Accordingly, the correlation values ofc₁(t) and c₂(t) are not merely compared; it is required that thecorrelation values be observed for a case where c₁(t) and c₂(t) areshifted arbitrarily in time.

[0019]FIG. 23 is a diagram showing the construction of a CDMAtransmitter which code-multiplexes and transmits data on a number ofchannels. This illustrates the construction of a prior-art base stationin wireless mobile communication, by way of example. As shown in FIG.23, the transmitter includes spread-spectrum modulators 11 ₁-11 _(n) of1st through nth channels, respectively. Each spread-spectrum modulatorincludes a frame generator 21, a serial/parallel (S/P) converter 22 forconverting frame data to parallel data, and a spreading circuit 23. Theframe generator 21 has a transmission data generator 21 a for generatingserial transmission data D₁, a pilot signal generator 21 b forgenerating a pilot signal which is peculiar to a base station, and aframe forming unit 21 c for forming the serial data D₁ (see FIG. 24)into blocks every prescribed number of bits and inserting the pilotsignal P at the beginning and end of each block, thereby producing dataframes. The frame generators 21 of each of the spread-spectrummodulators 11 ₁-11 _(n) insert identical pilot signals P into thetransmission data at the same timing. The purpose of the pilot signal Pis to allow the receiver to recognize the amount of phase rotation ofthe spread-spectrum modulated signal due to transmission. In otherwords, the pilot signals are used to perform de-spreading by allowingthe receiver to detect the amount of phase rotation of thespread-spectrum modulated signal in the transmission path from theposition of the transmitted pilot and the position of the receivedpilot, and to restore the phase of the spread-spectrum modulated signalby an amount equivalent to the amount of phase rotation.

[0020] The S/P converter alternately distributes the frame data (thepilot signals and transmission data) one bit at a time to convert theframe data to I-component (in-phase component) data D_(I) andQ-component (quadrature-component) data D_(Q), as shown in FIG. 24.

[0021] The spreading circuit 23 includes a pseudorandom noise (pn)sequence generator 23 a for generating a pn sequence (long spreadingcode) which is peculiar to the base station, an orthogonal Gold codegenerator 23 b for generating an orthogonal Gold code (short spreadingcode) for user identification, an EX-OR gate 23 c for obtaining theexclusive-OR between the pn sequence and the orthogonal Gold code andoutputting a resulting code C₁, and EX-OR gates 23 d, 23 e forperforming spread-spectrum modulation by obtaining the exclusive-ORsbetween the data D_(I) and D_(Q), respectively, and the code C₁. Itshould be noted that since “1” is level 1 and “0” is level −1, theexclusive-OR between signals is the same as the product between them.

[0022] Also shown in FIG. 23 are a combiner 12 i for outputting anI-component code-multiplexed signal ΣV_(I) by combining the I-componentspread-spectrum modulated signals V_(I) output by the respectivespreading circuits 11 ₁-11 _(n); a combiner 12 q for outputting aQ-component code-multiplexed signal ΣV_(Q) by combining the Q-componentspread-spectrum modulated signals V_(Q) output by the respectivespreading circuits 11 ₁-11 _(n); FIR-type digital chip shaping filters14 i, 14 q for limiting the bandwidths of the code-multiplexed signalsΣV_(I), ΣV_(Q), respectively; DA converters 14 i, 14 q for convertingthe digital outputs of the respective filters 13 i, 13 q to analogsignals; a quadrature modulator 15 for applying quadrature phase-shiftkeying (QPSK) modulation to the code-multiplexed signals ΣV_(I), ΣV_(Q)of the I and Q components and outputting the modulated signal; a poweramplifier 16 for amplifying the output of the quadrature modulator 15,and an antenna 17.

[0023] The quadrature modulator 15 includes a carrier generator 15 a foroutputting a carrier wave cos ωt having a prescribed frequency, a 90°phase shifter 15 b for shifting the phase of the carrier wave by 90° andoutputting −sin ωt, a multiplier 15 c for multiplying the output signalof the DA converter 14 i by cos ωt, a multiplier 15 d for multiplyingthe output signal of the DA converter 14 q by −sin ωt, and a combiner 15e for combining the outputs of the multipliers 15 c and 15 d.

[0024]FIG. 25 is a diagram showing the construction of the orthogonalGold code generator 23 b. The code generator 23 b includes a first M(maximum-length code) sequence generator 23 b-1, a second M sequencegenerator 23 b-2, an exclusive-OR gate 23 b-3 for obtaining theexclusive-OR between the first and second M sequences, and a “0” add-onunit 23 b-4 for adding a “0” onto the end of the sequence outputted bythe exclusive-OR gate 23 b-3.

[0025] The first M sequence generator 23 b-1 has a 6-bit shift registerSF1 and an exclusive-OR gate EOR1, generates the M sequence

A={a _(i) , i=0, 1, 2, . . . , N−2}

[0026] by performing the operation represented by a primitive polynomialX⁶+X+1 and adds “0” onto the end of the M sequence A, thereby generatinga sequence U, of sequence length N=2^(n), expressed by the followingequation:

U=(a ₀ , a ₁ , a ₂ . . . a _(N−2), 0)=(A,0)

[0027] The second M sequence generator 23 b-2 has a 6-bit shift registerSF2 and an exclusive-OR gate EOR2, generates the M sequence

B={b _(i) , i=0, 1, 2, . . . , N−2}

[0028] by performing the operation represented by a primitive polynomialX⁶+X⁵+X³+X²+1 and adds “0” onto the end of the M sequence B, therebygenerating a sequence V_(j), of sequence length N=2^(n), expressed bythe following equation:

V _(j) =[Tj(b ₀ , b ₁ , b ₂ . . . b _(N−2)), 0]=(T _(j) B,0)

[0029] where T_(j)B is the result of shifting the sequence B by j. Theorthogonal Gold code is produced from the sequences U, V_(j) and iscomposed of a set of N sequences.

[0030] The first M sequence generator 23 b-1 generates the sequence U(the initial value of the shift register SF1 being made 000001). Thesecond M sequence generator 23 b-2, on the other hand, generates thesequence B with ‘000000’ being the initial value of the shift registerSF2, and generates the sequence V_(j) by shifting the sequence B (N−1)times. Next, the exclusive-OR gate 23 b-3 obtains the exclusive-ORbetween the sequences U and V_(j) and outputs (N−1) items of data. Afterthe (N−1) items of data are output, the “0” add-on unit 23 b-4 outputs“0” as the N-th item of data, thereby generating a first orthogonal codesequence G₁.

[0031] Next, the first M sequence generator 23 b-1 generates thesequence U (the initial value of the shift register SF1 being made000001). The second M sequence generator 23 b-2, on the other hand,generates the sequence B with ‘000000’ being the initial value of theshift register SF2, and generates the sequence V_(j) by shifting thesequence B (N−2) times. Next, the exclusive-OR gate 23 b-3 obtains theexclusive-OR between the sequences U and V_(j) and outputs (N−1) itemsof data. After the (N−1) items of data are output, the “0” add-on unit23 b-4 outputs “0” as the N-th item of data, thereby generating a secondorthogonal code sequence G₂.

[0032] Thereafter, and in similar fashion, (N−2) sequences G₃-G_(N) aregenerated. As a result, a set of a total of N sequences G₁-G_(N) isobtained. A feature of these codes is orthogonality between the codesequences. FIG. 26 shows an example of 64 orthogonal Gold codesequences, each having a code length of 64 bits, generated in the mannerdescribed above. The last value of each sequence is “0”.

[0033] A multiplexed signal of pilots in a case where code multiplexinghas been performed using the above-mentioned orthogonal Gold codes withpilots in phase is expressed as follows, where the data dealt with is(−1, +1): $\begin{matrix}{\underset{pilot}{MultiCode} = {\sum\limits_{i}^{user}\left( {{ogold}_{i} \times {Pilot} \times {PN}} \right)}} \\{= {{Pilot} \times {PN} \times {\sum\limits_{i}^{user}\left( {ogold}_{i} \right)}}} \\{= {C \times {\sum\limits_{i}^{user}\left( {ogold}_{i} \right)}}}\end{matrix}\quad$

[0034] Consider the right side of this equation. The amplitude of themultiplexed signal takes on the maximum value at the portion where “0”is given as the Nth item of data when the orthogonal Gold codes aregenerated (“0” corresponds to the −1 level), as shown in FIG. 27. Thereason for this is that since the amplitude (the outputs of thecombiners 12 i, 12 q in FIG. 24) of a multiplexed signal in CDMA is thesum of the voltages of all multiplexed channels, the maximum value isobtained when the orthogonal Gold codes are all “0”s or all “1”s.

[0035] Thus, in pilot-insertion type CDMA, pilot signals are added onframe by frame and the pilot signals are spread-spectrum modulated byorthogonal codes (orthogonal Gold codes) for user identification and apn sequence. Let n represent the number of channels. After codemultiplexing n-number of spread-spectrum modulated signals that havebeen generated, a CDMA base station applies QPSK modulation and thentransmits the modulated signal. When the n channels of spread-spectrummodulated signals are code-multiplexed in such a CDMA base station, thepilot signals are in common for each of the channels and the outputtimings of the pilot signals of each of the channels are the same.Consequently, the power of the signal obtained by n-code multiplexingthe spread-spectrum modulated signals develops peak values at the pointswhere the pilot signals reside, as shown in FIG. 28. This is a problemin that these peaks of the multiplexed signal act as interference waveswith respect to other stations.

[0036] Another factor is that the input/output characteristic of a poweramplifier is linear up to a certain input level but becomes non-linearwhen this level is exceeded. FIG. 29 shows an example of an AM-AMcharacteristic (input power vs. gain characteristic) of a poweramplifier, and FIG. 30 shows an example of an AM-PM characteristic(input power vs. phase characteristic) of a power amplifier. It will beunderstood from these characteristic curves that the gain characteristicand phase characteristic of a power amplifier are flat and so is theinput/output characteristic as long as the input power is small. Thereis also no phase rotation under these conditions. However, when theinput power exceeds a certain level, gain starts to decline, a phase lagdevelops and each characteristic becomes non-linear. It is required touse a power amplifier with a high power efficiency and it is necessaryto raise the mean power level of the input signal. When the mean powerlevel of the input signal is raised, however, the peak value of thecode-multiplexed signal exceeds the linear region and saturates and thepeak values at the locations of the pilot signals are clipped, as shownin FIG. 31. As a result, when this code-multiplexed signal is de-spreadon the receiving side, the pilot signal power becomes small incomparison with the power of the other data, pilot detection errorincreases and the amount of phase rotation can no longer be recognized.The result is that data can no longer be demodulated correctly. If themean power level of the input signal is used upon being reduced, aproblem which arises is a decline in the power efficiency of the poweramplifier.

SUMMARY OF THE INVENTION

[0037] Accordingly, an object of the present invention is to reduce thepeak values of identical signal portions, e.g. the pilot signalportions, of identical timings in the code-multiplexed signal.

[0038] Another object of the present invention is to make it possible toreduce the power of radio waves which interfere with other stations,thereby increasing system capacity.

[0039] A further object of the present invention is to make efficientuse of the power amplifier.

[0040] In accordance with the present invention, the foregoing objectsare attained by providing a code multiplexing transmitting apparatus forspread-spectrum modulating transmission data of a plurality of channelsby spreading codes that differ from one another, combining thespread-spectrum modulated signals of each of the channels andtransmitting the resultant spread-spectrum modulated signal, comprisinga phase shifter for shifting, by a predetermined angle channel bychannel, phase of a signal-point position vector of the spread-spectrummodulated signal of each channel.

[0041] Other features and advantages of the present invention will beapparent from the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is a block diagram illustrating the principle of thepresent invention;

[0043]FIG. 2 is a diagram showing the construction of a codemultiplexing transmitter according to first embodiment of the presentinvention;

[0044]FIG. 3 is a diagram useful in describing the position vector of aspread-spectrum modulated signal;

[0045]FIG. 4 is a diagram for describing amount of phase shift;

[0046]FIG. 5 is a diagram useful in describing symbol positions inquadrature phase-shift keying modulation;

[0047]FIG. 6 is a diagram for describing symbol values (V_(I)′, V_(Q)′)after a phase shift;

[0048]FIG. 7 is a diagram useful in describing pilot symbol positionswhen amount of phase shift is made 2π·i/N;

[0049]FIG. 8 is a diagram showing the construction of a codemultiplexing transmitter according to a second embodiment of the presentinvention;

[0050]FIG. 9 is a diagram useful in describing a phase-shift controlvalue (amount of phase shift);

[0051]FIG. 10 is a diagram useful in describing a phase-shift controlvalue (amount of phase shift);

[0052]FIG. 11 is a diagram useful in describing pilot symbol positionswhen amount of phase shift is made 2π·i/N;

[0053]FIG. 12 is a diagram showing the construction of a codemultiplexing transmitter according to third embodiment of the presentinvention;

[0054]FIG. 13 is a diagram showing the construction of a codemultiplexing transmitter according to fourth embodiment of the presentinvention;

[0055]FIG. 14 is a diagram showing the construction of a codemultiplexing transmitter according to fifth embodiment of the presentinvention;

[0056]FIG. 15 is a diagram showing the construction of a codemultiplexing transmitter according to sixth embodiment of the presentinvention;

[0057]FIG. 16 is a block diagram illustrating the principle of atransmitter;

[0058]FIG. 17 is a diagram useful in describing the temporal waveformsof transmission data and a spreading code sequence;

[0059]FIG. 18 is a diagram useful in describing the spectrumdistribution of a spread-spectrum modulated signal;

[0060]FIG. 19 is a diagram for describing spreading ratio;

[0061]FIG. 20 is a diagram showing the principle of a receiver;

[0062]FIG. 21 is a diagram for describing de-spreading;

[0063]FIG. 22 is a diagram for describing the principle of CDMA;

[0064]FIG. 23 is a diagram showing the construction of a prior art CDMAtransmitter;

[0065]FIG. 24 is a diagram for describing frames;

[0066]FIG. 25 is a diagram showing the construction of an orthogonalGold code generating circuit;

[0067]FIG. 26 is a diagram for describing orthogonal Gold codes;

[0068]FIG. 27 is a diagram for describing amplitude when orthogonalcodes are multiplexed;

[0069]FIG. 28 is a diagram useful in describing the output power of amultiplexed signal when a prior-art method is used;

[0070]FIG. 29 is characteristic diagram showing the AM-AM characteristicof an amplifier; and

[0071]FIG. 30 is characteristic diagram showing the AM-PM characteristicof the amplifier; and

[0072]FIG. 31 is a diagram for describing the output power of atransmitting amplifier and transmission power after de-spreading.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (A) Overview of the Invention

[0073]FIG. 1 is a diagram useful in describing an overview of a codemultiplexing transmitting apparatus according to the present invention.

[0074] Spread-spectrum modulating units 51 ₁-51 _(n) of 1st -nthchannels each include a frame generator 61 for generating a frame signalby inserting pilot signals into transmission data every. predeterminednumber of items of data, a spreading code generator 63 for generating aspreading code, a spread-spectrum modulator 64 for spread-spectrummodulating the frame signal by-the spreading code, and a phase shifter65 for shifting, by a predetermined angle channel by channel, the phaseof a signal-point position vector of the spread-spectrum modulatedsignal. A code-multiplexed signal generator 52 multiplexes thespread-spectrum modulated signals of the respective channels, the outputof the code-multiplexed signal generator 52 is input to a modulator 55such as a quadrature phase-shift keying (QPSK) modulator, the output ofthe modulator 55 is applied to a transmitting power amplifier 56, andthe amplified signal from the amplifier 56 is input to an antenna 57.

[0075] Unless the signal-point position vectors of the spread-spectrummodulated signals of respective channels are shifted in phase, the pilotsignals will be the same on each of the channels and the output timingsof the pilot signals on each of the channels will be identical. As aconsequence, the power of the signal (the output signal of thecode-multiplexed signal generator 52) obtained by code-multiplexing thespread-spectrum modulated signals of respective channels will developpeak values at the pilot signal portions, these peak portions willproduce interference in other stations and the power efficiency of thepower amplifier will decline.

[0076] Accordingly, the phase shifter 65 in the spread-spectrummodulating unit 51 ₁-51 _(n) of each channel shifts, by a predeterminedangle channel by channel, the phase of the signal-point position vectorof the spread-spectrum modulated signal of each channel. For example,the phase shifter 65 of an ith channel makes the phase-shift angle θ ofthe ith channel equal to 360°·i/N and phase-shifts the position vectorby an amount equivalent to this phase-shift quantity θ, where Nrepresents the number of channels. Alternatively, the phase shifter 65of each channel stores amount of phase shift in correspondence withspreading codes, obtains an amount of phase shift that conforms to thespreading code used in spread-spectrum modulation and rotates the signalby an amount equivalent to the phase-shift quantity. If this arrangementis adopted, the phases of the pilot signal portions of thespread-spectrum modulated signals output by the spread-spectrummodulators 51 ₁-51 _(n) of the respective channels will be shiftedrelative to one another, thus making it possible to suppress the peakvalues of the code-multiplexed signal, reduce the power of interferencewaves and raise the power efficiency of the transmitting power amplifier56. In this case, the phases of the signal-point position vectors of thespread-spectrum modulated signals may be shifted by a prescribed anglewith regard to all transmission data and pilot signals, or the phases ofthe position vectors of the spread-spectrum modulated signals may beshifted by a prescribed angle with regard solely to the pilot signals.

[0077] Further, in case of QPSK spread-spectrum modulation, the amountof phase shift is made 0, π/2, π or 3π/2. More specifically, ifm=mod(i,4) holds (where m is the remainder obtained when i is divided by4), then (m·π/2) is adopted as the amount of phase shift for the ithchannel. If this arrangement is adopted, phase control can be carriedout in simple fashion.

[0078] The receiver will not be able to demodulate the data correctlyunless it is notified of the amount of phase shift. Accordingly, thereceiver is notified of the amount of phase shift for each channel by acontrol channel or by a special-purpose channel dedicated tonotification of amount of phase shift. Further, the data indicative ofthe above-mentioned amount of phase shift is inserted into the framesand these data are transmitted to the receiver along with thetransmission data.

[0079] Further, in a case where the frame signal is alternatelydistributed one bit at a time to thereby be converted to I-componentdata and Q-component data, the I-component data and Q-component data areeach spread-spectrum modulated by spreading codes, the spread-spectrummodulated signals of respective channels are multiplexed for every Icomponent and Q component, the code-multiplexed signals of the I and Qcomponents are quadrature modulated and then transmitted, the phaseshifter is provided between the spread-spectrum modulator andcode-multiplexed signal generator of each channel and the signal-pointposition vector in the I, Q rectangular coordinate system of thespread-spectrum modulated signal is shifted by a prescribed angle foreach channel. In this case, the phase shifter makes the phase-shiftangle e of the ith channel equal to 360°·i/N and shifts the phase of thesignal-point position vector by an amount equivalent to this phase-shiftquantity 0, where N represents the number of channels. Alternatively, ifm=mod(i,4) holds (where m is the remainder obtained when i is divided by4), then (m·π/2) is adopted as the amount of phase shift for the ithchannel.

(B) First Embodiment

[0080]FIG. 2 is a diagram showing the construction of a codemultiplexing transmitter according to a first embodiment of theinvention, e.g. a base station used in mobile wireless communication.This is an embodiment for a case where QPSK modulation is applied asordinary narrow-band modulation.

[0081] As shown in FIG. 2, the spread-spectrum modulating units 51 ₁-51_(n) of the 1st-nth channels each include the frame generator 61 forgenerating a frame signal by inserting pilot signals into transmissiondata every predetermined number of items of data, a serial/parallel(S/P) converter 62 for converting the frame data to parallel data, thespreading code generator 63 for generating a spreading code C_(i) (i=1,2 . . . n), the spread-spectrum modulator circuit 64 for spread-spectrummodulating the frame signal by the spreading code C_(i), and the phaseshifter 65 for shifting, by a predetermined angle θ for every channel,the phase of a signal-point position vector of the spread-spectrummodulated signal.

[0082] The frame generator 61 includes a transmission data generator 61a for generating serial transmission data D_(i) (i=1, 2, . . . n), apilot signal generator 61 b for generating a pilot signal Pperpendicular to a base station, and a frame forming unit 61 c forforming the serial data D_(i) into blocks every predetermined number ofbits and inserting the pilot signals at the beginning and end of eachblock to thereby form data frames. The frame generator 61 of each of thespread-spectrum modulating units 51 ₁-51 _(n) inserts identical pilotsignals P into the transmission data at identical timings.

[0083] The S/P converter 62 alternately distributes the frame data (thepilot signals and transmission data) one bit at a time to convert theframe data to I-component (in-phase component) data D_(I) andQ-component (quadrature-component) data D_(Q). The spreading-codegenerator 63 includes a pn sequence generator 63 for generating a pnsequence (long spreading code) specific to the base station, anorthogonal Gold code generator 63 b for generating an orthogonal Goldcode (short spreading code) for user identification, and an EX-OR gate63 c for obtaining the exclusive-OR between the pn sequence and theorthogonal Gold code and outputting the resulting code C_(i) (i=1, 2, .. . n). The spreading circuit 64 includes EX-OR gates 64 a, 64 b forperforming spread-spectrum modulation by obtaining the exclusive-ORsbetween the I- and Q-component data D_(I) and D_(Q), respectively, andthe code C₁. It should be noted that since “1” is level 1 and “0” islevel −1, the exclusive-OR between the signals is the same as theproduct between them.

[0084] The phase shifter 65 shifts the signal-point position vector ofthe spread-spectrum modulated signal by a prescribed angle θ for everychannel. If the spread-spectrum modulated signals V_(I), V_(Q) of the Iand Q components are plotted on a complex plane, the result is as shownin FIG. 3, where it is seen that the resultant vector V is thesignal-point position vector of the spread-spectrum modulated signal.

[0085] The peaks of the code-multiplexed signal occur at the portionswhere the spread pilot symbols are multiplexed. Accordingly, thesignal-point position vector of the spread-spectrum modulated signal ofeach channel is angularly rotated (shifted) by 0, π/2, π or 3π/2, asshown in FIG. 4, to scatter the signal-point positions of the pilotsignals of each channel. More specifically, the amount of phase shift θof the ith channel among the N channels is obtained in accordance withthe equation

θ=(π/2)·mod(i,4)  (1)

[0086] and the signal-point position vector v of the spread-spectrummodulated signal is rotated by the amount of phase shift θ, wheremod(i,4) is the remainder obtained when i is divided by 4. In accordancewith Equation (1), the amount of phase shift of the 0th channel is 0,the amount of phase shift of the first channel is π/2, the amount ofphase shift of the second channel is π, the amount of phase shift of thethird channel is 3π/2, and so on.

[0087] The phase shifter 65 includes a phase controller 65 a forcalculating the amount of phase shift θ of the ith channel in accordancewith the operation of Equation (1), and arithmetic units 65 b, 65 c forcalculating, in accordance with Equations (2) and (3) below, I and Qcomponents (symbols) V_(I)′, V_(Q)′ of a signal-point position vector V′resulting from rotation by θ:

V _(I) ′=V _(I)·cos θ−V_(Q)·sin θ  (2)

V _(Q) ′=V _(I)·cos θ+V_(Q)·sin θ  (3)

[0088] If the operations of Equations (2) and (3) are performed bytaking the symbol (00) in QPSK modulation in the first quadrant, thesymbol (10) in the second quadrant, the symbol (11) in the thirdquadrant and the symbol (01) in the fourth quadrant and expressing “1”by the +1 level and “0” by the −1 level, as illustrated in FIG. 5, thenthe symbols (V_(I)′,V_(Q)′) upon rotation by the phase quantities 0,π/2, πand 3π/2 will be as shown in FIG. 6. The numerical values withinthe parentheses are the levels. Accordingly, a correspondence tableshown in FIG. 6 giving the correspondence between the symbols(V_(Q),V_(Q)) before rotation and the symbols (V_(I)′,V_(Q)′) afterrotation through each of the amounts of phase shift can be stored inmemory beforehand. This will make it possible to obtain thephase-shifted I- and Q-components V_(I)′ and V_(Q)′ of the signal-pointposition vector V′ from the correspondence table without performing theoperations of Equations (2) and (3).

[0089] With reference again to FIG. 2, the combiner 52 i outputs anI-component code-multiplexed signal ΣV_(I)′ by combining the I-componentspread-spectrum modulated signals output by the respectivespread-spectrum modulating units 51 ₁-51 _(n), and a combiner 52 qoutputs a Q-component code-multiplexed signal ΣV_(Q)′ by combining theQ-component spread-spectrum modulated signals output by the respectivespread-spectrums modulating units 51 ₁-51 _(n). FIR-type digital chipshaping filters 53 i, 53 q limit the bandwidths of the code-multiplexedsignals ΣV_(I)′, ΣV_(Q)′, respectively, and DA converters 54 _(i), 54 qconvert the digital outputs of the respective filters 53 i, 53 q toanalog signals. The quadrature modulating units 55 applies QPSKmodulation to the code-multiplexed signals ΣV_(I)′, ΣV_(Q)′ of the I andQ components and outputs the modulated signal, a power amplifier 56amplifies the output of the quadrature modulating unit 55 and an antenna57 transmits the output of the amplifier.

[0090] The quadrature modulating unit 55 includes a carrier generator 55a for outputting a carrier wave cos ωt having a prescribed frequency, a90° phase shifter 55 b for shifting the phase of the carrier wave by 90°and outputting −sin ωt, a multiplier 55 c for multiplying the outputsignal of the DA converter 54 i by cos ωt, a multiplier 55 d formultiplying the output signal of the DA converter 54 q by −sin ωt, and acombiner 55 e for combining the outputs of the multipliers 55 c and 55d.

[0091] In accordance with the first embodiment, it is so arranged thatthe phase shifter 65 of each channel shifts the phase of thesignal-point position vector of the spread-spectrum modulated signal bythe angles 0, π/2, π, 3π/2 given by Equation (1). As a result, the pilotsignal portion is split up into four portions. Consequently, the peakvalues at the pilot signal portions of the code-multiplexed signal canbe reduced, the power of radio waves that interfere with other stationscan be reduced and the capacity of the system can be increased. Inaddition, the fact that the peak values of the code-multiplexed signalcan be made small makes it possible to enlarge the mean power of theinput signal to the transmitting power amplifier 56, thereby making itpossible to use the power amplifier efficiently.

[0092] The foregoing is for a case where the amounts of phase shift aremade the angles 0, π/2, π and 3π/2, which are given by Equation (1), andthe pilot signal portion of the code-multiplexed signal is dispersedinto four portions. However, an arrangement can be adopted in which thepilot signal portion is split up into N(>4) portions to enhance the peaksuppression effect. More specifically, it can be so arranged that thephase controller 65 a of the phase shifter 65 calculates the amount ofphase shift θ of an ith channel (ith user) in accordance with theequation

θ=360°·i/N (i=0, 1, . . . )  (4)

[0093] (where N represents the number of channels) and the arithmeticunits 65 b, 65 c execute the operations of Equations (2), (3) to rotate(shift the phase of) the signal-point position vector. If thisarrangement is adopted the amounts of phase shift in each channel can bemade to differ. As a result, the pilot signal portion of thecode-multiplexed signal can be split up into N portions so that the peakvalues of the code-multiplexed signal at the pilot signal portion can besuppressed satisfactorily.

[0094]FIG. 7 is a diagram useful in describing pilot symbol positions ofeach channel in a case where the pilot symbol is 00. Here. A is adiagram for describing pilot symbol position in a situation whereconventional phase control is not carried out and B is a diagram fordescribing pilot symbol position of each channel in a case where phaseshift by the angles given by Equation (4) is carried out in accordancewith the present invention. With the conventional method, pilot symbolpositions become superimposed and large peaks are produced at the pilotsignal portions of the code-multiplexed signal. By contrast, with themethod of the present invention, the pilot symbol positions do notbecome superimposed and, as a result, large peaks are not produced asthe pilot signal portions.

(C) Second Embodiment

[0095]FIG. 8 is a diagram showing the construction of a codemultiplexing transmitter according to a second embodiment of theinvention. This is an embodiment for a case where QPSK modulation isapplied as ordinary narrow-band modulation. Elements identical withthose of the first embodiment shown in FIG. 2 are designated by likereference characters.

[0096] The first embodiment deals with a case in which the phase of thesignal-point position vector of all transmission data and pilot signalsin the code-multiplexed signal is rotated. In the second embodiment,only the signal-point position vector of the pilot signals is rotated.

[0097] The second embodiment of FIG. 8 differs from the first embodimentof FIG. 2 in that

[0098] (1) a pilot position signal PPS indicating the pilot signalduration is input to the phase shifter 65 by the pilot generator 61 b,and

[0099] (2) the phase shifter 65 performs phase rotation control when thepilot position signal PPS is at the high level, thereby rotating thephase of the pilot symbol (the pilot signal-point vector) in accordancewith Equations (1)-(3).

[0100]FIG. 9 is a diagram useful in describing a phase control value(amount of phase shift). FIG. 9 illustrates control of phase rotationthrough the angles 0, π/2, π, 3π/2, given by Equation (1), appliedsolely to the pilot signal portions of the spread-spectrum modulatedsignal. Phase angle is not controlled at the data portions.

[0101] The foregoing is for a case where the amounts of phase shift aremade the angles 0, π/2, π, 3π/2 given by Equation (1), as a result ofwhich the pilot signal portion is split up into four portions. However,the peak suppression effect can be enhanced further by splitting up thepilot signal portion into N portions. More specifically, it can be soarranged that the phase controller 65 a of the phase shifter 65calculates the amount of phase shift θ of an ith channel (ith user) inaccordance with the Equation (4) (where N represents the number ofchannels) and the arithmetic units 65 b, 65 c execute the operations ofEquations (2), (3) to rotate (shift the phase of) the signal-pointposition vector solely of the pilot signal portions of thespread-spectrum modulated signal.

[0102]FIG. 10 is a diagram useful in describing a phase control value(amount of phase shift). FIG. 10 illustrates control of phase rotationthrough the angles θ₀-θ_(N−1) given by Equation (4), applied solely tothe pilot signal portions of the spread-spectrum modulated signal. Phaseangle is not controlled at the data portions.

[0103]FIG. 11 is a diagram useful in describing pilot symbol positionsof each channel in a case where the pilot symbol is 00. Here A is adiagram for describing pilot symbol position in a situation whereconventional phase control is not carried out and B is a diagram fordescribing pilot symbol position of each channel in a case where phaseshift control by the angles given by Equation (4) is carried out inaccordance with the present invention. With the conventional method,pilot symbol positions become superimposed and large peaks are producedat the pilot signal portions of the code-multiplexed signal. Bycontrast, with the method of the present invention, the pilot symbolpositions do not become superimposed and, as a result, large peaks arenot produced as the pilot signal portions.

[0104] If this arrangement is adopted the amounts of phase shift in eachchannel can be made to differ. As a result, the pilot signal portion ofthe code-multiplexed signal can be split up into N portions so that thepeak values of the code-multiplexed signal at the pilot signal portionscan-be suppressed satisfactorily.

(D) Third Embodiment

[0105] In the first and second embodiments, amount of phase shift iscalculated based upon Equation (1) or Equation (4). In the thirdembodiment, amounts of phase shift are brought into 1:1 correspondencewith orthogonal Gold codes (short codes), the amount of phase shift thatconforms to an orthogonal Gold code used in spread-spectrum modulationis obtained and the phase of the signal-point position vector is shiftedby the amount of this phase shift.

[0106]FIG. 12 is a diagram showing the construction of a codemultiplexing transmitter according to a third embodiment of theinvention. Elements identical with those of the first embodiment shownin FIG. 2 are designated by like reference characters. The thirdembodiment of FIG. 12 differs from the first embodiment of FIG. 2 inthat

[0107] (1) a pilot phase information storage table 66 is provided andstores the correspondence between orthogonal Gold code identificationnumbers and amounts θ of pilot phase shift, and

[0108] (2) the phase shifter 65 obtains, from the correspondence table,the amount of phase shift that corresponds to an orthogonal Gold codeused in spread-spectrum modulation and controls the rotation of thesignal-point position vector by this amount of phase shift.

[0109] The amount of phase shift θ corresponding to an ith orthogonalGold code is given by the following equation:

θ=(i−1)·2π/M  (5)

[0110] where M represents the number of orthogonal Gold codes.Accordingly, it is also possible to adopt an arrangement in which thephase controller 65 a is capable of deciding the amount of phase shift θby performing the operation of Equation (5) without using a table.

[0111] In accordance with the third embodiment, the amount of phaseshift is decided in dependence upon the orthogonal Gold code for useridentification. This means that the user need only be notified of theorthogonal Gold code, it being unnecessary to separately notify the userof the amount of phase shift. This makes it possible to eliminatecontrol for notifying of amount of phase shift.

(E) Fourth Embodiment

[0112] In a case where the signal-point position vector has been rotated(the symbol position has been phase-shifted) on the side of thetransmitter, the pilot cannot be detected accurately and precise datareconstruction cannot be carried out on the receiver side unless thereceiver is made to recognize the amount of phase shift. Accordingly,the fourth embodiment is so adapted that the receiver can be notified ofthe amount of phase shift.

[0113]FIG. 13 is a diagram showing the construction of a codemultiplexing transmitter according to a fourth embodiment of theinvention having means for giving notification of amount of phase shift.Elements identical with those of the first embodiment shown in FIG. 2are designated by like reference characters. This transmitter includes aspread-spectrum modulating unit 71 for the control channel. A mobilestation (MS) is shown at 81.

[0114] The spread-spectrum modulating unit 71 for the control channelincludes a control information generator 71 a, a pilot generator 71 b, aframe forming unit 71 c, an S/P converter 71 d, an orthogonal Gold codegenerator 71 e for generating a known orthogonal Gold code for thecontrol channel, and a spreading circuit 71 f. The control informationgenerator 71 a acquires and generates control information such as (1) anumber specifying an orthogonal Gold code used in each channel (by eachuser) and (2) the amount of phase shift θ in each channel. The frameforming unit 71 c forms the control data into blocks every predeterminednumber of bits and inserts the pilot signals P at the beginning and endof each block to thereby form data frames. The S/P converter 71 dalternately distributes the frame data (the pilot signals and controldata) one bit at a time to convert the frame data to I-component(in-phase component) data D_(I)′ and Q-component (quadrature-component)data D_(Q)′.

[0115] Exclusive-OR gates 71f_(I), 71f_(Q) of the spreading circuit 71 fperform spread-spectrum modulation by obtaining the exclusive-ORsbetween the I- and Q-component data D_(I)′ and D_(Q)′, respectively, andthe orthogonal Gold code.

[0116] In accordance with the fourth embodiment, one channel is used asa control channel and control information such as an orthogonal Goldcode identification number for user identification and the amount ofphase shift θ in each user channel is transmitted to the receiver sideusing the control channel.

[0117] Since the orthogonal Gold code used in the control channel andthe pilot signals inserted in the frames are already known in the mobilestation (on the terminal side) 8, the mobile station detects the pilotsusing the known orthogonal Gold code, obtains the amount of phaserotation θ in the transmission path of the spread-spectrum modulatedsignal of the control channel and then subsequently performsde-spreading by restoring, by the amount obtained (=θ), the phase of themodulated received spread-spectrum modulated signal, therebydemodulating the data. As a result, the mobile station 81 is capable ofobtaining the orthogonal Gold code identification number for useridentification and the phase rotation information (the amount of phaseshift θ_(i)) from the control channel.

[0118] The mobile station 81 thenceforth applies QPSK demodulationprocessing to the code-multiplexed signal sent from the base station,restores the I and Q components (the signal-point position vector) ofthe demodulated spread-spectrum modulated signal to the original byrotating these components in the opposite direction by the amount ofphase shift θ_(i) of which notification has been given via the controlchannel, and demodulates the pilot signals and transmission data byperforming de-spreading.

[0119] In a case where phase rotation solely of the pilot signal portionis performed on the transmitting side, as in the second embodiment, onlythe signal-point position vector of the pilot signal portion is restoredby being rotated on the receiving in the opposite direction by theamount of phase shift of which notification has been given, and thepilot signals and transmission data are demodulated by performingde-spreading.

[0120] An alternative method of transmitting the phase information tothe side of the mobile station is to prepare a special-purpose channel,which is separate from the control channel, for notification of phaseinformation and give notification of the phase information via thischannel.

(F) Fifth Embodiment

[0121] In the fourth embodiment, the receiver is notified of the amountof phase shift via a control channel or special-purpose channel forgiving notification of the phase information. In a fifth embodiment, themobile station is notified of phase information by a frequency differentfrom that, of the code-multiplexed signal.

[0122]FIG. 14 is a diagram showing the construction of the fifthembodiment, in which elements identical with those of the firstembodiment in FIG. 2 are designated by like reference characters.

[0123] The transmitter includes a transmitter 91 for giving notificationof phase information. The mobile station (MS) is shown at 81.

[0124] The transmitter 91 for notification of phase information includesa spread-spectrum modulating unit 92, chip shaping filters 93 i, 93 q,DA converters 94 i, 94 q, a QPSK quadrature modulator 95 for performingquadrature modulation using frequencies cos ω₁t, sin ω₁t different fromthe frequencies of the quadrature modulator 55, a transmitting poweramplifier 96 and an antenna 97. The spread-spectrum modulating unit 92includes a phase information generator 91 a, a pilot generator 91 b, aframe forming unit 91 c, an S/P converter 91 d, an orthogonal Gold codegenerator 91 e for generating a known orthogonal Gold code, and aspreading circuit 91 f. The phase information generator 91 a acquiresamount of phase shift θ_(i) in each channel (of each user) and generatesphase information. The frame forming unit 91 c forms the phase data intoblocks every predetermined number of bits and inserts the pilot signalsP at the beginning and end of each block to thereby form data frames.The S/P converter 91 d alternately distributes the frame data (the pilotsignals and phase information) one bit at a time to convert the framedata to I-component (in-phase component) data D_(I)′ and Q-component(quadrature-component) data D_(Q)′. Exclusive-OR gates 91f_(I), 91f_(Q)of the spreading circuit 91 f perform spread-spectrum modulation byobtaining the exclusive-ORs between the I- and Q-component data D_(I)′and D_(Q)′, respectively, and the orthogonal Gold code.

[0125] Since the frequency for notification of phase information, theorthogonal Gold code used in notification of the phase information andthe pilot signals inserted in the frames are already known in the mobilestation (on the terminal side) 81, the mobile station obtains the phaseinformation (amount of phase shift) from the already knownphase-information notification frequency. The mobile station 81thenceforth switches over the reception band to the code-multiplexedsignal bandwidth, applies QPSK demodulation processing to thecode-multiplexed signal sent from the base station, restores the I and Qcomponents (the signal-point position vector) of the demodulatedspread-spectrum modulated signal to the original by rotating them in theopposite direction by the amount of phase shift obtained above, anddemodulates the pilot signals and transmission data by performingde-spreading.

(G) Sixth Embodiment

[0126] In the fourth embodiment the receiver is informed of the amountof phase shift via control channel or special-purpose channel dedicatedto giving notification of the phase information. In a sixth embodiment,however, the phase information (amount of phase shift) of each channelis inserted in a frame and transmitted together with the pilot signalsand transmission data.

[0127]FIG. 15 is a diagram showing the construction of the sixthembodiment, in which elements identical with those of the firstembodiment in FIG. 2 are designated by like reference characters. Thisembodiment differs from the first embodiment in that

[0128] (1) a phase information generator 61 d is provided in the framegenerator 61;

[0129] (2) the amount of phase shift θ_(i) is input to the phaseinformation generator 61 d from the phase shifter 65; and

[0130] (3) the frame forming unit 61 c forms frames by forming theserial transmission data into blocks every predetermined number of bits,inserting the pilot signals at the beginning and end of each block andinserting the phase information after the pilot signals.

[0131] Initially the base station transmits the signal-point positionvector of the spread-spectrum modulated signal without rotating thevector (without performing phase control). The mobile station 81establishes synchronization between the base station and the mobilestation, subsequently detects the phase information (amount of phaseshift θ_(i)) within the frame and rotates the I and Q components (thesignal-point position vector) of the demodulated spread-spectrummodulated signal in the opposite direction by the amount of the phaseshift θ_(i) detected. On the other hand, the phase shifter 65 of thebase station rotates the signal-point position vector of thespread-spectrum signal by the amount of phase shift θ_(i) by suitablyselecting the timing at which the mobile station detected the amount ofphase shift θ_(i), and the quadrature modulating unit 55 subjects thecode-multiplexed signal to QPSK modulation and then transmits themodulated signal. As a result, the mobile station subsequently iscapable of restoring the I and Q components (the signal-point positionvector) of the demodulated spread-spectrum modulated signal to theoriginal by rotating them in the opposite direction by the amount ofphase shift θ_(i) detected, and of demodulating the pilot signals andtransmission data by performed de-spreading.

[0132] In accordance with the sixth embodiment, phase control is notcarried out until the phase information is detected. After the phaseinformation is detected, however, phase control is performed so that thepeaks of the code-multiplexed signal can be suppressed.

[0133] In accordance with the present invention, it is so arranged thatthe phase of the signal-point position vector of a spread-spectrummodulated signal is shifted by a prescribed angle every channel. As aresult, even if identical pilots are generated by the frame generator ofeach channel at identical timings, the phases of the pilot signalportions of the spread-spectrum modulated signals output by thespread-spectrum modulators of the respective channels will be staggeredand dispersed relative to one another, thus making it possible tosuppress the peak values of the code-multiplexed signal, reduce thepower of interference waves and raise the power efficiency of thetransmitting power amplifier.

[0134] Further, in accordance with the present invention, the amounts ofphase shift are made 0, π/2, π and 3π/2 in case of QPSK spread-spectrummodulation. As a result, control of phase can be carried out in simplefashion.

[0135] Further, in accordance with the present invention, the amount ofphase shift in each channel can be made different by making the amountof phase shift θ_(i) of the ith channel equal to i·2π/N. This makes itpossible to disperse the pilot signal portions of the code-multiplexedsignal so that the amount of suppression of peak values can be enlarged.

[0136] Further, in accordance with the present invention, it is soarranged that the receiver side is notified of the amount of phase shiftof each channel by a control channel or by a special-purpose channeldedicated to giving notification of the amount of phase shift. As aresult, the receiver is capable of demodulating pilot symbols and datasymbols correctly.

[0137] Further, in accordance with the present invention, it is soarranged that data giving notification of the amount of phase shift isinserted into frames and transmitted to the receiver side together withthe transmission data. As a result, the receiver side can be notified ofthe data representing the amount of phase shift through simple control.

[0138] Further, in accordance with the present invention, amounts ofphase shift are brought into 1:1 correspondence with spreading codes(orthogonal Gold codes) beforehand and a phase shifter obtains theamount of phase shift that conforms to an orthogonal Gold code used inspread-spectrum modulation and rotates the phase of the signal-pointposition vector by the amount of this phase shift. As a result, theamount of phase shift can be decided in simple fashion. Moreover, thereceiver side need only be notified of the originally required spreadingcode (orthogonal Gold code) used in de-spreading and it is unnecessaryto inform of amount of phase shift separately. As a result, control forgiving notification of amount of phase shift can be eliminated, therebysimplifying control.

[0139] As many widely different embodiments of the present invention canbe made without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

What is claimed is:
 1. A code multiplexing transmitting apparatus forspread-spectrum modulating transmission data of respective channels byspreading codes that differ from one another, combining thespread-spectrum modulated signals of each of the channels andtransmitting the resultant spread-spectrum modulated signal, comprising:a phase shifter for shifting phase of a signal-point position vector ofthe spread-spectrum modulated signal of each channel by a predeterminedangle channel by channel.
 2. The apparatus according to claim 1, whereinsaid phase shifter shifts the phase of the signal point position vectorof the spread-spectrum modulated signal of each channel by apredetermined angle only in a case where the spread-spectrum modulatedsignals of respective channels carries identical data at identicaltimings.
 3. The apparatus according to claim 2, wherein said phaseshifter makes an amount of phase shift θ of an ith channel equal to360°·i/N, where N represents the number of channels.
 4. The apparatusaccording to claim 2, wherein amounts of phase shift are brought into1:1 correspondence with the spreading codes and said phase shifterobtains the amount of phase shift that conforms to a spreading code usedin spread-spectrum modulation and rotates the phase of the signal-pointposition vector by the amount of this phase shift.
 5. The apparatusaccording to claim 2, further comprising means for notifying a receiverside of amount of phase shift of each channel by a control channel or bya special-purpose channel dedicated to giving notification of amount ofphase shift.
 6. The apparatus according to claim 2, further comprising:means for inserting data, which notifies a receiver side of the amountof phase shift, into the transmission data; and means for transmittingthe data representing the amount of phase shift to the receiver sidetogether with the transmission data.
 7. The apparatus according to claim1, wherein said phase shifter makes the prescribed angle equal to 0,π/2, π or 3π/2 in a case where QPSK spread-spectrum modulation isperformed.
 8. The apparatus according to claim 7, wherein (m·π/2) isadopted as amount of phase shift of an ith channel, where m=mod(i,4)holds (where m is the remainder obtained when i is divided by 4).
 9. Theapparatus according to claim 8, wherein said phase shifter shifts thephase of a signal-point position vector of the spread-spectrum modulatedsignal of each channel by a prescribed angle only in a case where thespread-spectrum modulated signals of respective channels carriesidentical data at identical timings.
 10. The apparatus according toclaim 1, wherein said phase shifter determines the number ofsignal-point based upon the number of channels used.
 11. A codemultiplexing transmitting apparatus for spread-spectrum modulatingtransmission data of respective channels by spreading codes that differfrom one another, combining the spread-spectrum modulated signals ofeach of the channels and transmitting the resultant spread-spectrummodulated signal, comprising: a spread-spectrum modulating unit providedfor each channel for outputting a respective spread-spectrum modulatedsignal;. multiplexers for respectively multiplexing in-phase componentsand quadrature components of the spread-spectrum modulated signals ofeach channel outputted by the spread-spectrum modulating units; aquadrature modulator for quadrature modulating the code-multiplexedsignals of the in-phase and quadrature components; and a transmitter fortransmitting the signal modulated by said quadrature modulator; saidspread-spectrum modulating unit of each channel including: means forforming frames by forming transmission data into blocks every prescribednumber of bits and inserting pilot signals at the beginning and end ofeach block; means for alternately distributing, one bit at a time, theframe signals to thereby convert in-phase. component data and quadraturecomponent data; means for respectively spread-spectrum modulating thein-phase component data and quadrature component data by spreadingcodes; and phase shifting means for shifting phase of a signal-pointposition vector in an I (in phase), Q (quadrature) rectangularcoordinate system of the spread-spectrum modulated signal by aprescribed angle.
 12. The apparatus according to claim 11, wherein saidphase shifter makes an amount of phase shift θ of an ith channel equalto 360°·i/N, where N represents the number of channels.
 13. Theapparatus according to claim 11, wherein (m·π/2) is adopted as amount ofphase shift θ of an ith channel, where m=mod(i,4) holds (where m is theremainder obtained when i is divided by 4).